1. Field of the Invention
The present invention concerns an installation for the manufacture of containers from a preform and a method of controlling blow-molding means of such an installation.
The invention concerns more particularly an installation for manufacturing containers, in particular bottles, by blow-molding or by stretch-blow-molding from a thermoplastic material preform, the installation including at least:                a preform feeding device adapted to feed an entry of the installation with preforms,        a thermal conditioning unit including at least one oven including means for heating preforms arranged between an entry area to which the preforms are fed by the feed device and an exit area which opens into a transfer area of the installation,        a first transfer device in the transfer area adapted to transfer thermally conditioned preforms from the exit area of the oven to a feeding area of a molding unit,        the molding unit including a wheel equipped with a plurality of molds distributed in the circumferential direction and associated blow-molding or stretch-blow-molding means, the wheel being driven in rotation so that each mold follows a transformation cycle from said feed area to a evacuation area,        a second transfer device in the transfer area adapted to transfer containers obtained from the evacuation area of the molding unit to an exit of the installation, and        a control device adapted to control movement of the blow-molding or stretch-blow-molding means that include at least one nozzle associated with each mold.        
2. Description of the Related Art
Many installations of this type are known in the art, and include at least one molding unit equipped with a control device for the blow-molding or stretch-blow-molding means adapted to control movement of at least one nozzle that is associated with each mold carried by the wheel of the molding unit.
As is known in the art, the nozzle is generally arranged above the mold and mounted to move vertically between at least two end positions, respectively a top or waiting position and a bottom or blow-molding position.
The top position of the nozzle corresponds to an open position of the mold, i.e. the position that each mold occupies when it is in the feed area or the evacuation area to allow respectively the initial introduction of the preform and the final evacuation of the container obtained after the transformation cycle.
Conversely, the bottom position of the nozzle corresponds to the closed position that each mold occupies during the cycle of transforming the preform into a container that is carried out on the wheel between said feed and evacuation areas.
In the bottom position, the mold being closed, the nozzle caps at least one orifice of the mold through which the neck of the preform passes. This orifice is provided in a horizontal top wall of the mold, for example, and is adapted to allow the neck of the preform to pass through it when the blow-molding unit is operating with preforms in the “neck at top” position.
When the mold is closed, the neck of the preform projects above the wall while the body, which extends vertically under the neck, is received inside the mold.
In such an installation, movement of the blower nozzle is commanded selectively by the control device because descent from the top or waiting position to the bottom or blow-molding position is effected only if a preform is introduced into the mold.
Now, either intentionally or unintentionally, it is possible for the stream of preforms to include a “gap”, i.e. an empty space on the transfer means that is reflected by an absence of any preform in the feeding area, as a consequence of which no preform can be introduced into the mold.
By way of example there are cited the situation in which a given application uses only alternate molds on the blow-molding wheel, in particular because of the required container output rate, which is determined as a function of the timing of a filling unit downstream of the exit from the installation, for example, and the situation in which a preform is eliminated because of non-conformance, in particular non-conformance of its heating profile, which can be checked in the transfer area by means of a thermal camera type device.
Nevertheless, even if no preform is introduced, the wheel continues to operate to continue the transformation cycle in progress in the other molds so that the empty mold in the feed area is shifted by one step to the next station at a rate determined to be necessary for synchronizing the units of the installation.
The molding unit usually includes actuating means, for example of the mechanical type, for opening and closing the molds and which cause automatic opening and closing synchronized with the transformation cycle, in particular closing of the mold in the feed area and, conversely, opening of the mold in the evacuation area.
Accordingly, independently of the presence or the absence of a preform, each mold is automatically closed by the actuating means.
However, in the case of a missing preform, an empty mold is not in fact closed when it is in the closed position as the orifice is open because the blow-molding means remain in the top position because of the missing preform.
It is possible for the interior of the mold and the external environment to communicate via this orifice.
This is why there is a risk of airborne particle contamination of the empty mold, in particular by germs, bacteria, etc. present in the surrounding atmosphere and liable to contaminate the interior of the mold and consequently preforms and containers subsequently manufactured by the contaminated mold.
Such risks of contamination are unacceptable in installations in which a constant concern is to improve hygiene because of ever stricter demands in respect of the sterile or aseptic nature of the containers manufactured.